Back when I was young I was all about Degrassi Jr. High and BH 90210.
As an adult I liked:
Veronica Mars. A densely plotted noir combined with character-driven drama combined with sharp dialogue and wit. The pilot set up so many mysteries and while some paid off better than others, the overall ride was worth it. The second season got too stuffed and the third was a network-meddled mess that's worth forgetting. One thing to note about the third season was this was a rare teen show that made the move to college work.
The O.C. The theme song, the casting aside from Mischa Barton, the mix of high drama, class struggles and heartfelt familial bonding, The O.C. was brilliant. In fact, I hate when people call this show a guilty pleasure because it was smarter than it had any right to be.
Gossip Girl GG had some of the same elements of The O.C. but the heart was darkened and replaced with the icy coldness of a dagger. I bailed after the beginning of S2 had the wonderful Madchen Amick playing a desperate cougar and the show seemed to embrace it's mean side. It's pampered rich kid fantasy world also felt a bit dated and shallow compare to the next two shows, which have forever altered my ability to enjoy a teen series.
Skins While the show takes teen hedonism to fantastical heights, Skins is grounded by likeable characters played by loveable actors with problems that are more realistic and richer. I found few characters on TV more layered and wonderful than Hannah Murray's Cassie. What's best was the diverse group of kids from S1 and 2, not just ethnically diverse but diverse in their beliefs and goals, formed a believeable unit where they transcended being friends and were more like family. That's what teen bonding is like. S3 swapped out the cast and while it was good in its own right, it lacked the strength of the first two series. Still, this is a show that few people in the US know about and its a shame because its really worth watching over and over again.
Friday Night Lights I think this show surprised the crap out of me like it did everyone else. A show about high school football sounded like a dumb idea but of the series that are currently on the air this is my favorite. Over Lost and 24 and True Blood and Flashforward and Glee. The fourth season just started last week on DirecTV and while most of the teens have moved on, the core of the show, Coach Taylor and his wife Tami, are stronger than ever. From the verite filming style to the music inspired by the Austin band Explosions in the Sky this show is about big ideas told in intimate ways. The naturalistic acting of the cast and the realistic dialogue that has teens saying "ummm" a lot and articulating grand emotions using a limited vocabulary, FNL transcends television and becomes televised literature, in a way that few series (The Wire and The West Wing are two I can think of) can ever hope to achieve.